Stressed concrete structures and method of making

ABSTRACT

A prestressed concrete structure wherein a body of set concrete has at least one reinforcing rod therein. One end of the rod is restrained and the other end of the rod has abutment means thereon. The length of the rod between the abutment means and the restrained end is of predetermined magnitude. After the concrete is set, the rod is heated so that it expands longitudinally permitting a spacer of predetermined length to be inserted between the abutment of the rod and the concrete thereby producing a predetermined stress on the rod.

United States Patent Campbell 1 July 18, 1972 STRESSED CONCRETE STRUCTURES 2,058,364 10/1936 Sorensen ..s2/231 I AND METHOD OF MAKING 2,535,100 12/1950 Sourwine.... .....52/223 R X 2,804,674 9/1957 Long ..52/223 L X [72] Inventor: Henry Fred Campbell, Bellevllle, Mich. Y 73] Assignee: Campbell Research Corporation, Detroit, FOREIGN PATENTS OR APPLICATIONS Mich. 541,835 12/1941 Great Britain ..52/741 746,617 3/1956 Great Britain .....52/223 R 1 Wed 1,231,091 4/1960 France .;52/223 [21] Appl. No.: 41,935

Primary Examiner-Alfred C. Perham Attorney-Barnes, Kisselle, Raisch & Choate [52] US. Cl. ..52/223 R, 52/230, 52/741,

264/223 [57] ABSTRACT [51] Int. Cl. ..E04c 3/10, 1504c 3/26 [58] Field of Search ..52/223, 224, 230, 741 223 R A Prestressed concrete Structure 0f set 52/223 264/27 concrete has at least one reinforcing rod therein. One end of the rod is restrained and the other end of the rod has abutment 56] References Cited means thereon. The length of the rod between the abutment means and the restrained end is of predetermined magnitude. UNITED STATES PATENTS After the concrete is set, the rod is heated so that it expands longitudinally permitting a spacer of predetermined length to 312901840 12/1966 Mddendorf "52/223 be inserted between the abutment of the rod and the concrete 2,319,105 5/1943 B1llner ---5 X thereby producing a predetermined stress on the rod. 3,422,586 1/1969 Parrna... ..52/23O 3,293,811 12/1966 Rice ..52/223 L 6 Claim, 13 Drawing Figures Wes 311% PATENTEU JUL 1 8 an 3,676; 968

MM, M M

9 Z? ATTORNEYS PATENTEU JUL 1 8 I972 SHEET 3 OF 3 FIG.

INVENTOR F/PfD CAM/ 512.4

ATTORNEYS STRESSED CONCRETE STRUCTURES AND METHOD OF MAKING This invention relates to reinforced concrete slabs and particularly to concrete slabs which are stressed after the concrete is set.

BACKGROUND OF THE INVENTION.

A common method of making prestressed concrete slabs comprises embedding reinforcing rods in a body of concrete and thereafter applying stress to the rods by mechanical means after the concrete has been set. This has proved generally satisfactory but requires special mechanical equipment.

It has heretofore been suggested that a method of expanding the reinforcing rods might be used by electrical heating as set forth in the patent to Billner US. Pat. No. 2,319,105. However, this has not proved practical commercially satisfactory.

Among the objects of the invention are to provide a novel prestressed concrete structure and a novel method of making such structure; novel prefabricated slab structures and novel methods of making said slabs; and a novel stressed concrete deck and a novel method of making said deck.

SUMMARY OF THE INVENTION A prestressed concrete structure wherein a body of set concrete has at least one reinforcing rod therein. One end of the rod is restrained and the other end of the rod has abutment means thereon. The length of the rod between the abutment means and the restrained end is of predetermined magnitude. After the concrete is set, the rod is heated so that it expands longitudinally permitting a spacer of predetermined length to be inserted between the abutment on the rod and the concrete thereby producing a predetermined stress on the rod.

Where prestressed slabs are to be made, one end of each rod is completely embedded in the concrete while the other end having the abutment means thereon extends beyond the concrete. The embedded ends of adjacent rods are electrically connected and each pair of rods is simultaneously heated by.

applying current across the other ends of the rods which carry the abutment means. After heating, the aforesaid spacers are inserted between the abutment means and the concrete-In a preferred form, the adjacent pair of rods is electrically connected by an integral portion between the embedded ends.

Where it is desired, to provide a stressed concrete deck in a place in a building, each rod is preferably provided across beams and the concrete is poured leaving both ends of the rods accessible for electrical energy but the one end of the rod restrained against longitudinal movement and the other end which has abutment means thereon free to move longitudinally. Electrical current is then applied across each rod to cause it to expand longitudinally permitting insertion of the spacer means. In such a structure, each rod would be successively stressed until the entire deck is stressed.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view through an apparatus for making the reinforced concrete slabs showing parts in position;

FIG. 2 is a view similar to FIG. 1 showing the concrete after it has been poured;

FIG. 3 is a part sectional longitudinal view showing the slab in completed condition;

FIG. 4 is a fragmentary view taken along the line 44 in FIG. 3;

FIG. 5 is a fragmentary sectional view taken along the line 5-5 in FIG. 1;

FIG. 6 is a partly diagrammatic plan view showing the rod during the poststressing;

FIG. 7 is a part sectional plan view of a modified form of apparatus;

FIG. 8 is a sectional view taken along line 8-8 in FIG. 7;

FIG. 9 is a perspective view of a portion of the apparatus shown in Figs. 7 and 8;

FIG. 10 is a fragmentary plan view of a further modified form of the invention;

FIG. 11 is a fragmentary elevational view of the form of the invention shown in FIG. 10;

FIG. 12 is a fragmentary sectional view taken along the line 12-12 in FIG. 10 showing a portion of the parts after the concrete is poured;

FIG. 13 is a partly diagrammatic plan view of the form of the invention shown in FIGS. 11-12 during the post stressing.

DESCRIPTION Referring to FIG. 1, an apparatus for making the prestressed concrete slab in accordance with the invention comprises a form or mold 10 comprising a bottom wall 11, end walls 12' and side walls 13 to form a generally rectangular open top cavity that is many times longer than its width or height.

One end wall 12 includes a plurality of projections 14 thereon for receiving the reinforcing rods 15. as presently described. Each reinforcing rod 15 has a sheath or tube 16 of thermoplastic material such as polyethylene surrounding substantially the entire length thereof. One end 17 of each rod is held in position so that it will be completely embedded by the concrete and the ends 17 are permanently electrically connected as shown in FIG. 4 by plates 18 welded to the rods. each plate being electrically connected to the adjacent one by smaller rods 19 that are welded to the plates. The rods 15 are held in vertically spaced relation to the bottom of the mold by spacers 20 which, may comprise V-shaped plates .having openings 21 therein to permit the free passage of the concrete. The other end of each said rod 15 is supported by a projection 14.

After the rod assembly with plates 18 and small rods 19 is placed in proper position, the concrete is poured as shown in FIG. 2 and permitted to set.

The resultant partially completed slab has a cavity 22 formed by projection 14 into which the other end of each rod 15 projects.

Referring to FIG. 6, the hardened slab is removed from the mold and electrical energy from a source 24 is applied to the free ends 23 of the rods. Sufficient energy is applied to heat the rods and cause them to expand longitudinally. The plastic 16 permits free longitudinal movement of the rods relative to the body of concrete.

When the rods have been expanded sufficiently, a spacer 26 is interposed between plate 25 and the nut 27 on the rod and the nut 27 is tightened to clamp the spacer against the plate. The electrical current is then removed permitting the rods to cool and resulting in the longitudinal stressing of the rods. Finally, filler material 28 is applied to fill each cavity 22 resulting in the final prestressed concrete slab.

In the form of the invention shown in FIGS. 7-9, a plurality of slabs are formed simultaneously in a mold with the width of each slab extending generally vertically. As shown in FIG. 7, mold 30 comprises a side wall 31 and walls 32, 33 and intermediate walls 34, 35, 36. The mold further includes a bottom wall 37. Each of the walls 31-36 are re movable to provide access to the finally set slabs.

Each of the walls 34, 35, 36 is identical and includes destructible blocks 38 and a destructible spacer block 39 which may be made of foam plastic.

In the form shown, the reinforcing rods 40 are provided from asingle piece of stock with an integral interconnecting portion 41. The ends 42 of the rods 40 are threaded and nuts 43 are threaded onto the ends 42 to the full extent of the threads so that each rod 40 is of predetermined length. Each pair of rods 40 with the integral portion 41 and a plastic sheath thereon is supported by a wall 34, 35 or 36, by spacer 39 and blocks 38 which have countersunk openings 44 for receiving the ends 42 and nuts 43. This spaces the rods within the cavity of the mold.

After the concrete is set, the blocks 38 are removed by gouging out. The walls 3136 are then removed so that the slabs are accessible providing access to ends 42 from the sides of the slabs for application of electrical current. As in the previous form of the invention, by providing electrical current, the ends 42 are extended, the inner ends of the rods being restrained by the embedded integral portion 41. Spacers 45 are then inserted between the nuts 43 and the concrete, and the heating is interrupted permitting the rods to contract and placing the rods under predetermined stress. if desired, metal plates may be embedded in the concrete block so that the spacers 45 will abut against a surface which distributes the force over a greater area of concrete.

in the form of the invention shown in FIGS. -13, a stressed concrete deck is to be formed as for example, on the floor of a building. As shown, the building comprises spaced horizontal beams 50. A form 51 is provided between the beams as a temporary form for pouring the concrete. Rods 52 are positioned between pairs of beams as shown at longitudinally spaced points. Each rod 52 is threaded at both ends. Each end extends through a grommet 54 positioned in an opening 55 of an angle 56 welded to the beam 50. A nut 57 is threaded on one end of each rod. Each rod is further provided with a plastic sheath tube 58 as in the previous forms of the invention. The other end 59 of each rod is threaded and a nut 60 is threaded onto the threaded end 59 to the full extent so that there is a predetermined length of rod between the nuts 57, 60. Finally, spacer blocks 61, 62 of foam plastic or other destructible material are positioned on the ends 59, 52, respectively. The vertical block 62 is such that the concrete will embed the nut 57 sufficiently to restrain the nut but insufficient to interfere with electrical connection of the nut.

The concrete is then poured and permitted to set (FIG. 12). The resultant structure comprises a complete concrete deck with a plurality of rods embedded therein. The blocks 61, 62 at the ends of the rod are removed and electric power is ap plied to one rod. As the rod expands, the end 59 thereof and the nut 60 thereon will move away from its angle 56 permitting insertion of a spacer of predetermined width so that when the heating is discontinued the rod will contract and since it is of predetermined length a predetermined stress will be provided on each rod.

The heating of each rod and insertion of the spacer means is continued successively on each rod until all of the rods are placed under stress and as a result the entire deck will be under stress.

Iclaim:

1. The method of making reinforced concrete structures which comprises placing a plurality of electrically conducting rods across structural beams with one end thereof restrained from longitudinal movement with respect to one beam and the other end free,

supporting and electrically isolating said rods from said beams,

forming abutment means on the other end of each said rod,

pouring on said concrete about said rods in a manner such that said other ends are longitudinally unrestrained and said one ends are restrained but exposed and accessible, permitting said concrete to set,

thereafter applying heat to each said rod to expand said rod longitudinally of said concrete,

and placing spacer means between the abutment on each rod means and said set concrete,

said spacer means having a predetermined length whereby when the rod is permitted to cool, said predetermined length of rod is placed under predetermined stress.

2. The method set forth in claim 1 wherein said formation of said abutment means is achieved by threading a nut on the other end of said rod.

3. The method set forth in claim 2 including the step of making said thread of said rod of predetermined length and threading said nut on said rod to the full extent of said thread whereb the portion of the rod between the thread and the one en thereof forms the portion of predetermined accurate length.

4. The method set forth in claim 1 wherein said step of applying heat to said rods is achieved by applying electrical energy to the ends of said rod.

5. A prestressed concrete structure which comprises a body of set concrete,

a plurality of electrically conducting rods embedded in said body,

one end of said rods being restrained in said body,

abutment means on the other ends of said rods,

spacer means between the abutment means on said rods and said body,

said spacer means having a predetermined length,

said portion of said rods between said abutment means and said restrained end being under stress,

the length of said rods between said abutment means and said restrained end being of predetermined length whereby the stress in said rod is of predetermined magnitude,

a plurality of spaced horizontal beams, said body of concrete extending over said beams, said plurality of said rods extending longitudinally and transversely of said body,

means extending from said beams and embedded in said body, said ends extending through and electrically insu lated from said last mentioned means.

6. A prestressed concrete structure which comprises a body of set concrete,

an electrically conducting rod embedded in said body,

one end of said rod being restrained in said body,

abutment means on the other end of said rod,

spacer means between the abutment means on said rod and said body,

said spacer means having a predetermined length,

said portion of said rod between said abutment means and said restrained end being under stress,

the length of said rod between said abutment means and said restrained end being of predetermined length whereby the stress in said rod is of predetermined magnitude,

a pair of spaced beams,

said body of concrete extending over said beams,

means supporting and electrically insulating said rods from said beams. 

1. The method of making reinforced concrete structures which comprises placing a plurality of electrically conducting rods across structural beams with one end thereof restrained from longitudinal movement with respect to one beam and the other end free, supporting and electrically isolating said rods from said beams, forming abutment means on the other end of each said rod, pOuring on said concrete about said rods in a manner such that said other ends are longitudinally unrestrained and said one ends are restrained but exposed and accessible, permitting said concrete to set, thereafter applying heat to each said rod to expand said rod longitudinally of said concrete, and placing spacer means between the abutment on each rod means and said set concrete, said spacer means having a predetermined length whereby when the rod is permitted to cool, said predetermined length of rod is placed under predetermined stress.
 2. The method set forth in claim 1 wherein said formation of said abutment means is achieved by threading a nut on the other end of said rod.
 3. The method set forth in claim 2 including the step of making said thread of said rod of predetermined length and threading said nut on said rod to the full extent of said thread whereby the portion of the rod between the thread and the one end thereof forms the portion of predetermined accurate length.
 4. The method set forth in claim 1 wherein said step of applying heat to said rods is achieved by applying electrical energy to the ends of said rod.
 5. A prestressed concrete structure which comprises a body of set concrete, a plurality of electrically conducting rods embedded in said body, one end of said rods being restrained in said body, abutment means on the other ends of said rods, spacer means between the abutment means on said rods and said body, said spacer means having a predetermined length, said portion of said rods between said abutment means and said restrained end being under stress, the length of said rods between said abutment means and said restrained end being of predetermined length whereby the stress in said rod is of predetermined magnitude, a plurality of spaced horizontal beams, said body of concrete extending over said beams, said plurality of said rods extending longitudinally and transversely of said body, means extending from said beams and embedded in said body, said ends extending through and electrically insulated from said last mentioned means.
 6. A prestressed concrete structure which comprises a body of set concrete, an electrically conducting rod embedded in said body, one end of said rod being restrained in said body, abutment means on the other end of said rod, spacer means between the abutment means on said rod and said body, said spacer means having a predetermined length, said portion of said rod between said abutment means and said restrained end being under stress, the length of said rod between said abutment means and said restrained end being of predetermined length whereby the stress in said rod is of predetermined magnitude, a pair of spaced beams, said body of concrete extending over said beams, means supporting and electrically insulating said rods from said beams. 